Diesel Trouble Codes

P0299 — Turbocharger/Supercharger Underboost Condition (6.4 Power Stroke)

P0299 indicates boost pressure is below the minimum expected for current conditions on the 6.4L Power Stroke 2008-2010 twin sequential fixed-geometry compound…

Updated September 2, 2026

What it means

The PCM detects actual boost lower than expected for engine load/RPM. On this platform the 6.4L uses twin sequential fixed-geometry compound turbos with no VGT/vanes. Underboost can be a boost leak, sensor/electrical fault, or turbo mechanical issue.1234

Most likely causes

  1. Boost pressure sensor or MAP/Baro circuit fault — Erroneous low boost reading from a faulty boost pressure sensor, wiring, or reference (baro) causing PCM to set underboost. Verify sensor values vs. a known-good reference and check wiring/connectors for corrosion or chafing.134
  2. Boost leak in intake or intercooler plumbing — Leak between low-pressure and high-pressure turbos, intercooler, boots, or intake manifold reduces measured boost. Inspect charge-air piping, intercooler, and connections for cracks, loose clamps, or oil-soaked boots; pressure-test the boost system.14
  3. Turbocharger mechanical wear or damage — Worn bearings, damaged compressor/turbine wheels, or excessive shaft play in either the high-pressure or low-pressure turbo reduces boost output. Inspect turbocharger shaft play, wheel damage, and oil supply/return for restriction or contamination.123
  4. Exhaust restriction affecting turbine drive — Restricted DPF/DOC or exhaust blockage limits turbine speed and boost. On 6.4L, DPF restriction codes include P2002, P244A, P244B, P2463, P246C. Check exhaust backpressure and DPF differential pressure readings.14
  5. Intake air flow system performance deviation — Measured intake airflow outside expected range can contribute to underboost detection. Verify MAF/MAF-related data and intake restrictions such as a clogged air filter or intake blockage.5

How to diagnose

  1. Confirm code and freeze-frame conditions; verify boost pressure PID vs. desired boost under load.
  2. Inspect boost pressure sensor, MAP, and barometric sensor circuits for proper voltage, ground, and signal; compare readings to a scan tool reference.
  3. Perform a visual and pressure test of the entire charge-air system: turbo outlets, intercooler, boots, and intake manifold for leaks.
  4. Check turbocharger mechanical condition: shaft play, wheel damage, oil supply/return, and inspect for foreign object damage.
  5. Review exhaust backpressure and DPF differential pressure PIDs; inspect DPF/DOC for restriction per platform DPF codes.
  6. Verify intake airflow data and inspect air filter and intake for restriction; confirm no intake leaks upstream of turbos.

Parts and tools you may need

Rough cost and difficulty

Diagnostic time varies; repairs range from sensor replacement and hose/clamp repair to turbocharger replacement or DPF service. Actual cost depends on findings.

When to see a pro

If turbocharger replacement, DPF removal/service, or internal engine inspection is indicated, have a qualified diesel technician perform the work. Do not disassemble high-pressure fuel or turbo oil systems without proper training and safety precautions.

Sources

  1. Curated DTC seed — 6.4 Power Stroke (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — 6.4 Power Stroke (curated) ↩︎ ↩︎

  3. Curated DTC seed — 6.4 Power Stroke (curated) ↩︎ ↩︎ ↩︎

  4. Curated DTC seed — 6.4 Power Stroke (curated) ↩︎ ↩︎ ↩︎ ↩︎

  5. Curated DTC seed — 6.4 Power Stroke (curated) ↩︎

Watch a repair

Third-party videos, not ours — for illustration. Confirm anything against the factory service information for your truck.

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